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Building Tips and technical articles. => Paint and finishing => Topic started by: Ron Vargo on November 03, 2021, 04:22:26 PM

Title: Brodak dope on an aluminum spinner
Post by: Ron Vargo on November 03, 2021, 04:22:26 PM
Hey guys just returning to the CL Circle.  I haven’t painted with dope in a while.   Does anyone know if dope can be painted directly on an aluminum spinner or do I need etching  primer first    Thx
Title: Re: Brodak dope on an aluminum spinner
Post by: Ron Vargo on November 05, 2021, 05:47:48 PM
Thx for the tip
Title: Re: Brodak dope on an aluminum spinner
Post by: Warren Wagner on November 07, 2021, 12:18:34 PM
Ron,

One of our top builders/finishers did a write up on painting an aluminum spinner
in Stunt News, sometime before it was discontinued (I sure miss it).  I'm sorry,
but I don't remember what issue that was in, but perhaps this will jog someone's
memory that is better than mine.

A dope finish will obviously not last long if an electric starter is used, so I hope you
are a "hand starter".

It would be useful to "the hanger" if you would report back on your findings.

Cheers.

Warren Wagner
Title: Re: Brodak dope on an aluminum spinner
Post by: Avaiojet on November 07, 2021, 01:42:07 PM
Here's two spinners I painted on two models I designed from scratch.

Both models have a "Build" and the spinner painting detail is included in the "Builds." I think.

I believe the "Builds" are over at CFC Graphics in the vendor's corner.

Be advised there are tricks and shortcuts.

CB
Title: Re: Brodak dope on an aluminum spinner
Post by: Dennis Toth on November 07, 2021, 02:27:15 PM
With an aluminum spinner why is this any different from regular auto body painting? Seems if you use prep with reasonable surface prep (like sanding with 600) then prime and paint, clear coat (with death paint) just like a car? don't use electric starter and should be good to go.

Best,    DennisT
Title: Re: Brodak dope on an aluminum spinner
Post by: Avaiojet on November 07, 2021, 03:03:21 PM
With an aluminum spinner why is this any different from regular auto body painting? Seems if you use prep with reasonable surface prep (like sanding with 600) then prime and paint, clear coat (with death paint) just like a car? don't use electric starter and should be good to go.

Best,    DennisT

I wouldn't trust 600, but that's me. especially with a taped multi colored spinner which represents something. In my case, an actual aircraft. You also have to keep paint off the backplate where it meets the spinner and I don't paint the inside hole for the spinner nut.

Do this right and you won't have to sand the paint for a perfect chipless fit. I love saving steps.

Title: Re: Brodak dope on an aluminum spinner
Post by: Dan McEntee on November 07, 2021, 04:22:51 PM
With an aluminum spinner why is this any different from regular auto body painting? Seems if you use prep with reasonable surface prep (like sanding with 600) then prime and paint, clear coat (with death paint) just like a car? don't use electric starter and should be good to go.

Best,    DennisT

   Aluminum is constantly oxidizing, never stops, and will cause paint to flake all by itself. That is why you use an etching primer to help with adhesion. A good scuffing on bare aluminum will help with straight paint of any kind. A visit to a store that sells aircraft painting supplies will have what you need. I have never tried to buy it at an auto paint store but they may have it.

   Type at you later,
    Dan McEntee
Title: Re: Brodak dope on an aluminum spinner
Post by: Avaiojet on November 07, 2021, 04:58:12 PM
   Aluminum is constantly oxidizing, never stops, and will cause paint to flake all by itself. That is why you use an etching primer to help with adhesion. A good scuffing on bare aluminum will help with straight paint of any kind. A visit to a store that sells aircraft painting supplies will have what you need. I have never tried to buy it at an auto paint store but they may have it.

   Type at you later,
    Dan McEntee

Thank you, very important, real zinc chromate primer. I don't remember where I purchased mine but, it's available in aerosol cans.

A quick call to your local airport paint shop could get you a free can and these guys have this stuff around for small jobs. They will tell you where to get it.

Real aircraft supply stores
Title: Re: Brodak dope on an aluminum spinner
Post by: Jerry Rauch on November 11, 2021, 04:43:29 PM
The easiest and least expensive would be DupliColor Self Etching Primer #1690 available in spray cans at O'Reilly Auto parts stores. I believe it's $7.00 a can. It is the light olive green color. Clean first, sand with 400 for some "tooth", spray 2 coats, let dry overnight, sand with 400 or 600 before you put your color on.
I used this product in 2004 as primer on aluminum race car trailer fenders before single stage black, to this day, still there, except the black is somewhat faded since it sits in the sun all day.
Realized I forgot something, in using this paint, make sure you spray it outside, if in a closed in area, you may feel some burning in the eyes, it has some type of acid in it, hence, etching primer
Title: Re: Brodak dope on an aluminum spinner
Post by: doug coursey on November 19, 2021, 08:32:08 AM
i have painted a lot of aluminum parts for rc helicopters like tail boom and skids and would glass bead the part  and then use an etch primer.I never had it peel off and it took a lot of beating..
Title: Re: Brodak dope on an aluminum spinner
Post by: Brett Buck on December 15, 2021, 10:28:32 AM
     As an additional bit of information, epoxy primer seems to stick to bare aluminum pretty well, but for some reason, the color over the primer seems to have significantly reduced adhesion. Normally, epoxy paint over epoxy primer cannot be removed without sanding them both off, but over aluminum, it seems to affect the bond between the layers, and I have had it peel the color away from the primer, leaving the primer intact.

    I have no idea why this happens but its very consistent. Otherwise, the paint sequence is the same as the rest of the airplane, and done at the same time, so the aluminum must be causing it somehow. I have just been being careful and repairing it when necessary, but have been looking for other solutions, like etching primer.

      Brett
Title: Re: Brodak dope on an aluminum spinner
Post by: Jim Hoffman on December 15, 2021, 03:44:16 PM
Reply #9 from Jerry Rauch is spot on.
Remember that if you wish to match a color and tone, the undercoat colors must also be the same.
Here’s a Veco Alum spinner.  Randolph dope, auto urethane top clear coat